(1) to study the infectivity, stability and protective capacity of ts mutants of M. pneumoniae (strain PI 1428) in the hamster animal model and in man; (2) to study the effect of route of administration, site of colonization, dose and particle size of inoculum on the development of M. pneumoniae disease and subsequent immunity; (3) to develop a simian model for M. pneumoniae disease for use in studies of pathogenesis and immunity as well as for vaccine safety testing.